1. Field of the Invention
The present invention generally relates to a technology concerning the bandwidth of semiconductor opto-electronic devices, and more particularly, to a technology employing different separate confinement heterostructures (SCH's) of different lengths and/or non-identical multiple quantum wells such that the semiconductor photo-electronic devices have broad bandwidth, better temperature characteristics and more reliable modulation characteristics.
2. Description of the Related Art
With the arrival of the network era, indispensable components for use in fiber-based networks, such as transmission terminals, receiving terminals, switching terminals, etc., have attracted tremendous attention in both research and commercial applications. Semiconductor devices have become the major players in fiber communication due to their small sizes, high efficiency and high frequency handling ability, and high reliability (in both temperature and lifetime). The functions for relaying optical signal amplification and optical switching of semiconductor optical amplifiers (SOA's)/superluminescent diodes (SLD's) have been widely used. However, the conventional semiconductor optical amplifiers only provide a spectral width of about 40 nm, which is insufficient for wide-band fiber communication.
On the other hand, even though Er-doped fiber amplifiers (EDFA's) are widely used as relaying optical signal amplifiers in optical communication, they cannot be employed in another important band around 1300 nm due to the limitation of the available spectral width between C-band and L-band, i.e., 1525 nm˜1605 nm. This makes the application of the Er-doped fiber amplifier unable to cover the whole range between 1200 nm˜1600 nm of fiber communication. Therefore, there is need in providing a new relaying optical signal amplifier that has a wider band.
The device characteristics such as the threshold current density, the temperature dependence and the spectral width for the gain of a semiconductor quantum well laser are better than those of a bulk semiconductor laser. The thin epitaxial layers that form the quantum well structure, be it for research or commercial application, can be grown by metal-organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE). By using the conventional semiconductor fabrication process, semiconductor lasers can be formed of such a quantum well structure.
According to the recently published reports, however, the carriers generated by current injection do not distribute uniformly in the multiple quantum wells. If we want to increase the spectral width for the gain, uniformity of carrier distribution must be taken into account. In the prior art, several efforts have been made to increase the spectral width for the gain by using asymmetric multiple quantum well implementation without considering the uniformity of carrier distribution. However, the results are far from satisfactory.
Therefore, the inventors of the present invention proposed a technology employing multiple quantum wells of different widths so as to utilize the energy levels and the non-uniformity of carrier distribution in the multiple quantum wells to obtain a very large spectral width for the gain. In such a manner, the semiconductor optical amplifier of the present invention can cover the broad spectral width of 1300 nm˜1600 nm. In addition, by using separate confinement heterostructures of a certain wavelength, the dominant carriers controlling the two-dimensional carrier distribution could be either electrons or holes, leading to a wider spectral width for the gain as well as better temperature characteristic.